Liquid toners for electrophotography containing 12-hydroxy stearin

ABSTRACT

A LIQUID TONER FOR USE IN AN ELECTROPHOTOGRAPHIC PROCESS WHICH COMPRISES A SUSPENSION OF CHARGED PIGMENT PARTICLES IN AN INERT LIQUID CARRIER, THERE BEING DISPERSED IN THE SUSPENSION 12-HYDROXY STEARIN.

United States Patent Office 3,701,731 Patented Oct. 31 1972 Int. cl. G03g 9/04 US. Cl. 25262.1 3 Claims ABSTRACT OF THE DISCLOSURE A liquid toner for use in an electrophotographic process which comprises a suspension of charged pigment particles in an inert liquid carrier, there being dispersed in the suspension l2-hydroxy stearin.

This invention relates to the developing or toning of electro photographic images on electrophotographic material.

In the usual electrophotographic process after an imagewise exposure of the charged electrophotographic material the charge remains on the unexposed areas but is dissipated in the exposed areas so forming a differential charge pattern. The charge pattern on the electrophotographic material then is made visible by applying to it charged pigment particles of opposite polarity. When it is required to obtain an image having good resolution it is preferred to use pigment particles dispersed in a liquid. Such liquid developers for electrophotographic material are referred to hereinafter as liquid toners.

Liquid toners usually comprise charged pigment particles suspended in an insulating carrier liquid for example inert paraflin. Various additives may be added to improve the quality of the toner for example oils, metal salts and resins may be added to control the charge on the particles and assist in dispersing the particles in the carrier. There is usually present a resin which acts to fix the particles to the print material when the liquid carrier is evaporated and antioxidants are often also added to the toner to improve its shelf life.

One failing of liquid toners is that they tend to give low maximum densities, for example for a voltgae of 400 v. on the surface of the print material it is often possible to obtain a density of only 1.1 (diffuse reflection density) even when employing a high concentration of pigment in r the toner. It is possible that this density is determined by the charge to mass ratio of the pigment particles so that not enough pigment is attracted to the surface to obtain a higher density. When the voltage on the print material surface is relatively high, i.e. greater than 400 v., it is thought that the maximum density is restricted by the surface reflection of the pigment itself and that it is not possible to obtain a density much greater than 2. However by use of the liquid toner of the present invention it is possible to obtain maximum densities closer to the supposed greatest maximum density obtainable in these conditions, i.e. 2 than by use of the previously known liquid toners.

According to the present invention there is provided a liquid toner for use in an electrophotographic process which comprises a suspension of charged pigment particles in an inert liquid carrier, there being dispersed in the suspension 12 hydroxy-stearin.

12-hydroxystearin is also known as glycerol tris-12 hydroxystearate, or as glyceryl-tri-12 hydroxystearate. It is a waxy solid. It is present in the toner of the present invention dispersed in the inert liquid carrier. A suitable form of 12 hydroxstearin is marketed by Cray Valley Products Limited under the name of C.V.P. Antisettle and by Prices of Bromborough under the name of Synthawax when in flake form and as Pendol when in powder form.

The preferred liquid carrier is an inert liquid parafiin. The preferred parafiinic liquid carriers for use in the liquid toner of the present invention are the liquid paraffins manufactured and marketed by the Esso Chemical Limited as Isopar. The most preferred Isopar is known as Isopar G.

There may also be present in the liquid toner of the present invention the additives previously mentioned, that is to say oils, metal salts, resins and antioxidants.

The following example will serve to illustrate the present invention.

EXAMPLE A liquid toner containing the following ingredients was prepared:

Black positive toner formulation Microlith Black C-T-2 g. Mitchalac 204-0.8 g. Ferric stearate-0.05 g. C.V.P. Antisettle-1 g. Isopar G--18 ml.

The Mitchalac 204 and ferric stearate were first dissolved in Isopar G. the C.V.P. Antisettle and the Microlith Black C-T then added, and the suspension was ball milled for 16 hours. For use the suspension was diluted to 500 ml. with Isopar G.

Microlith Black GT is a predispersed black toning pigment consisting of carbon black and hydrogenated rosin ester manufactured by CIBA and described in Ciba Pattern Book No. 5090 (1968) and also described in r the Condensed Chemical Dictionary, 8th edition, Van

Nostrand Reinhold Co.

Mitchalac 204 is a long oil alkyd resin based on dehydrated castor oil and manufactured by W. A. Mitchell & Smith Limited.

C.V.P. Antisettle (12 hydroxy sterin) is manufactured by Cray Valley Products Limited, St. Mary's Cray, Kent.

Isopar G is an odourless paraffin manufactured by Esso Chemical Limited, Portland House, London, S.W. 1. The product is further characterized as a narrow-cut isoparafiinic hydrocarbon fraction boiling in the range 320-350 F.

The toner was compared to a liquid toner which was similar in all respects except that the C.V.P. Antisettle was not present.

Samples of electrophotographic material which comprised zinc oxide particles coated onto paper having a degree of electroconductivity were imagewise exposed to a wedge image and the samples were then treated using the toner. The results given are the diffuse reflection densities measured on a densitometer.

TABLE After 10 weeks Initial results standing in diluted torm Dmu. Dmin- Dmax- Dinin- Toner Appearance (400 v.) (0 v.) Appearance (400 v.) (0 v.)

No. C.V.P. entisettle Good dispersion... 0. 96 0. 02 Loose fioccnlate. 0. 69 0. 02 With C.V.P. antlsettle ..'.do 1. 58 0. 08 Good dispersion...

3. A liquid toner of claim 1, wherein the inert liquid carrier is a liquid isoparafiinic hydrocarbon.

This shows that the maximum density obtained using the liquid toner of the present invention, i.e. the toner with the C.V.P. Antisettle present gave very much better results that theliquid toner which did not comprise the C.V.P. Antisettle.

We claim as our invention:

1. A liquid toner for use in an electrophotographic process comprising an inert liquid hydrocarbon carrier selected from the ,group consisting of a liquid paraffinic hydrocarbon and a liquid isoparaflinic hydrocarbon having suspended therein a charged pigment consisting of carbon black and hydrogenated rosin ester and also dispersed therein 12-hydroxy stearin to efiect maximum image density.

2. A liquid toner for use in an electrophotographic process according to claim 1 wherein the inert liquid carrier is a liquid paraflinic hydrocarbon.

References Cited UNITED STATES PATENTS OTHER REFERENCES Chemical Index, vol. 49, column 638(e) (1955).

GEORGE F. LESMES, Primary Examiner 15 J. -P. BRAMMER, Assistant Examiner US. Cl. X.R. 

